Читать книгу Chevrolet Small-Block Parts Interchange Manual - Revised Edition - Ed Staffel - Страница 8

CHAPTER 2

GASKETS AND FASTENERS

When it comes to sealing your small-block Chevy, there several areas you’ll need to address due to design changes. First, you must determine whether you are building an engine using the familiar two-piece rear main oil seal or with the new-style one-piece rear main seal that was first introduced in Gen I blocks in 1986. Adapters are available, both from Chevrolet Performance and aftermarket suppliers, which allow you to use a one-piece, rear-main-seal-style block with an earlier two-piece seal crank.

When searching for gaskets, it is important to note that many different materials and applications are available from Chevy and aftermarket suppliers. Also, Chevrolet has discontinued many different gaskets and seals over the years but gasket companies such as Fel-Pro Gaskets, SCE Gaskets, Cometic Gaskets, and others that specialize in sealing engine components may have exactly what you’re looking for.

There are a variety of intakes and heads available, so make sure you have the correct intake setup for your application. Most GM intake manifolds are supplied with rubber end gaskets that fit on the block between the two head surfaces. Many aftermarket manifolds recommend using a gasket sealer instead.

Intake Manifold Gaskets

There are now five different production intake manifold gasket types, and which one you use depends on whether you are building a Gen I, Gen II LT1, Gen II LT4, or Vortec small-block. The intake manifold bolt angles, the bolt spacing, and the position in the cylinder heads and intake manifolds, and some production port positions have been altered from what you may be familiar with. Coolant crossover passages have been moved or in some motors eliminated. These intake manifold/head bolt hole changes began with the 1987 models. Intake manifold gaskets of interest include the following:

PN 10147994 fits all Gen I 262 to 400 small-blocks with standard port locations and sizes. This gasket does not work with 1996-or-later Vortec heads or intake manifolds. Do not use this intake manifold gasket on Gen II motors. This gasket has a heat riser passage. Using an intake manifold gasket with a blocked heat riser passage can help keep the temperatures in the intake manifold cooler; however, blocking the heat riser passage makes cold morning operation more difficult.

The PN 19301685 Intake Gasket is designed for the Chevrolet Performance Fast Burn Aluminum Vortec heads (PN 12558060, PN 19300955, and PN 19300956) only. The gaskets are 0.120-inch thick and have both the early six-bolt pattern and the Vortec four-bolt pattern.

For production Vortec heads, use gasket PN 89017465 with four bolt attachments to the heads. This installation requires attaching bolt PN 12550027 because the bolt has a ball design on the end that sits in the head so it will not crush the intake manifold gasket.

Many aftermarket gaskets are available with larger intake port openings, but unless you’ve port matched your intake and heads for all-out performance, stick with the original sizes.

Chevrolet used a variety of carbs and intakes over the years, which means there are a lot of different gaskets. On many of the intake manifolds made in the 1960s, a heat riser channel was cut across the carb mounting deck, which required a traditional gasket and a metal gasket. Newer-model gaskets do not seal these. In short, be aware of the year of the intake you are using to get the correct carburetor gasket.

If you plan to swap an LT1 (Gen II) engine to accept a carburetor and distributor, use intake gasket PN 12524653.

PN 12528884 is made for Gen II 350 LT4 raised intake port heads. There is no coolant passage in the gasket because these are reverse-flow heads. The manifold bolt holes have also been relocated (used on engine PN 12371172).

Chevrolet Performance offers other unique intake gaskets for use with different performance and racing cylinder heads. PN 10185042 is required with splayed valve heads (PN 24502517). For 18-degree high port heads (PN 10134363 and PN 24502580), use gasket kit PN 10185007.

Aftermarket gasket makers also can supply intake manifold gaskets with larger port openings for racers who are using heads with large port opening dimensions. Be sensible here. Don’t buy the largest intake port gasket you can get, thinking that if you open the port opening to the gasket size, you’ll improve the performance of the engine.

If you are building a street engine, the only thing you need to remember is to make sure that the intake manifold port opening and head port opening match and that there is no ledge formed by the gasket or the head to impede flow. If you are building a race motor and you have substantially improved the flow in the port runners and increased the size of the head port opening, think about increasing the gasket size opening to match the port sizes.

Carb Gaskets

Over four decades of small-block production, a number of different carburetors have been used, and all these carburetors used different-style gaskets between the carb base and the top surface of the intake manifold.

Heat riser passages were built into some intake manifolds to feed warm air to the base of the carb to warm it up when first started on cold mornings. The carb gaskets must match the heat riser passages in these manifolds. You can check the intake manifold casting date to help determine which carburetor and carb gasket are correct for your application. The intake may require the use of a Rochester 2-barrel, Carter WCFB or AFB, Rochester Four Jet, Rochester Quadrajet, or Holley 4-barrel. One of the more common misapplications I have seen is the use of a later-style Quadrajet carb gasket on a 1969 or earlier Quadrajet intake, which has cast-in heat riser passages and a channel that runs across the front side of the carb mounting surface. This channel requires a particular carb gasket to seal it. If a later-style Quadrajet gasket is used on the 1969 and earlier intakes, the result is an air leak, because the later gasket doesn’t seal the intake surface and the heat riser channel completely.

Chevrolet used to offer two types of carb heat shields that fit between the intake manifold and the base of the carb and incorporate a carb gasket into the heat shield. PN 3969835 fit Holley square-flange 4-barrels and PN 3969837 fit Rochester Quadrajet spreadbore carbs on 1970-on intakes. These heat shields can reduce heat absorption by carb fuel bowls and can cure some fuel percolation problems. Aftermarket models are available.

Head Gaskets

Most production engines that have cast-iron heads were built using factory steel shim head gaskets. Engines with aluminum heads always received a composition-style head gasket. Composition head gaskets can be used with iron heads, but never use a steel shim gasket with aluminum heads.

Head gaskets are made in various compressed thicknesses and bore sizes. Altering the thickness of the gasket affects the measured static compression ratio of the engine. It also affects the clearance between the open valves and pistons and between the piston deck and the head deck. You need a minimum of 0.035- to 0.040-inch clearance between the piston deck and the head quench area deck with steel rods. When using aluminum rods, your engine may need more piston-deck-to-head-deck clearance to accommodate aluminum rod stretch.

Bolts, Studs, and Torquing Tips

Unless you’re building a turbocharged or supercharged engine that sees extended periods of severe service in a race car or a boat, there is little reason to use cylinder head studs. Studs are needed to ensure even gasket crush and promote proper sealing in engines with very high cylinder pressures. The brake mean effective pressure (BMEP) in the average street engine rarely approaches the point where gasket integrity is threatened. Blown head gaskets are normally the result of improperly torqued bolts, detonation, or improperly faced surfaces on the head or block.

For street and bracket racing applications, it is usually safe to use stock Chevy head bolts. Factory fasteners have the proper elasticity to provide effective clamping at the recommended torque specs. Aftermarket bolts—such as those available from ARP or Milodon, and others—perform very well.

If you angle-cut the heads to gain compression, be certain to have the machinist spot face all the head bolt seats to make them parallel to the deck surface. Remember also that the bosses along the outside of the head for the short bolts can get very thin after angle milling. It is possible to break or crack the head in this area if care is not exercised when torquing the bolts.

Another good move is to install the head and gasket on the bare block and observe their relationship through the empty cylinders. In this manner, you can determine if any part of the gasket or combustion chamber is overhanging the bore. This problem can be remedied by using the correct head gasket for your bore size and by lightly blending the edges of the combustion chambers to match the bore size. ■

Steel shim or copper gaskets must be coated with a head gasket sealer before installation.

The head gaskets for a 400 small-block have six additional steam holes between the cylinder barrels to help keep these siamesed blocks cool.

Some gaskets do not require hot re-torquing. However, it is not a bad idea to do a hot re-torquing on any head gasket. Follow the recommended head bolt torquing sequence and torque to the proper amounts.

PN 3830711 is a production steel shim gasket for 4-inch-bore Gen I engines. It is 0.026-inch thick when compressed and should only be used with cast-iron cylinder heads.

PN 10105117 is a composition head gasket with stainless steel surfaces. This gasket is used on 4-inch-bore Gen I motors and has a 0.028-inch compressed thickness. It can be used with cast-iron or aluminum heads and is recommended for marine engine use.

PN 12557236 was used on the ZZ4 crate engine and other 350 HO engines. This composition gasket has a compressed thickness of 0.051 inch and can be used with other cast-iron or aluminum heads and 4-inch bores.

PN 10185054 is a heavy-duty, competition composition gasket that is Teflon coated with solid wire fire rings. Compressed thickness is 0.040 inch and it should be used with 4.0- to 4.165-inch-bore Gen I blocks. This gasket does not have any steam holes for use on street-driven siamesed bore 400 blocks. If used on the street, drill the steam holes in the gasket and use heads with steam holes.

PN 14096405 composition gasket has a stainless steel face on one side and graphite coating on the other. Compressed thickness is 0.028 inch and it is for 4-inch-bore Gen I blocks.

PN 10168457 is a composite head gasket for the 1992–2001 aluminum headed LT1 engine. It has a compressed thickness of 0.050-inch.

If you are building a siamesed 400 production block and you intend to use the motor on the street, you need to use a 400-style head gasket with extra steam holes and be sure there are matching steam holes in the heads you use. If the heads you intend to use do not have the required steam holes in their deck, you can use a 400 head gasket as a template to locate and drill the six extra steam holes in each head. If you are going to race a 400 small-block full-time, there is no need to drill the matching steam holes in the heads. Coolant flow at engine speeds above 3,500 rpm is sufficient to keep things cooled down.

Chevrolet Performance offers a Cylinder Head Installation Kit for the 5.7L L31 engine (1986 and newer Gen I engines). PN 12499223 is supplied with two head gaskets (PN 10105117), two center-bolt valve cover gaskets (PN 10046089), and intake (PN 89017465) and exhaust gaskets (PN 12550033).

When overhauling an engine, it’s best to go with a complete gasket set. Chevy Performance offers two kits that are supplied with gaskets for the following surfaces: heads, oil pan, intake, rear main seal housing, water outlet, front cover, fuel pump adapter, water pump, valve covers, distributor, and rear main seal. Kit PN 19201171 is for the 350 HO, HT383, and Circle Track crate engines (PN 88958602 and PN 88869602). Gasket Kit PN 19201172 is designed for the Fast Burn 385, ZZ5, SP383/350, and ZZ6.

Valve Cover Gaskets

For decades, the Gen I small-block was notorious for valve cover oil leaks. When the new center-bolt valve covers were introduced in 1987, valve cover leaks were prevented by using a new mating surface and gasket on the covers and a machined gasket surface on the rails on the cylinder heads. If you have the old-style valve covers, you can use a bar retainer (plain steel PN 14082321 or chrome PN 14044820) to help the bolts hold down the cover by distributing the clamping force over a greater area. There is also a torx stud (PN 14082320) and nut (PN 14051876) for the older type of flange bolted cover, which makes mounting the valve cover gaskets easier.

The old-style cork valve cover gasket, used from 1955 to 1986, is PN 3933964. The gasket for center-bolt valve covers is PN 10046089. Each bolt on the center bolt valve covers has a small O-ring gasket under the bolt head which is available new as a kit with PN 12497980.

Clearances
Main Bearings	0.002 to 0.003 inch
Crank End Thrust	0.005 to 0.007 inch
Rod Bearings	0.002 to 0.0025 inch
Rod Side Clearance	0.010 to 0.020 inch
Piston to Bore	Follow recommendations of piston maker
Valve Lash	Follow recommendations of cam maker
Minimum Piston Ring End Gap	Follow recommendations of ring maker
Minimum Piston Deck to Head Deck	0.035 to 0.040 inch with steel rods, more may be needed with aluminum rods
Open Valve to Piston Deck	Minimum of 0.045 inch on a stock engine, 0.100 inch on a high-performance or race engine
Spark Plug Gap
0.035 inch with GM point ignition
0.045 inch with GM HEI ignition
0.035 to 0.060 inch with GM/MSD ignition
Cam End Play with Cam Button	0.004 to 0.006 inch

This is a traditional oil pan gasket set for a Gen I engine with a two-piece rear main seal. You need to get the pan gaskets that match the dipstick bulge location on your block and pan. Then determine whether your pan needs either the thin or thick front pan gasket. The 1955 to 1975 blocks and pans used the thin, 1/4-inch rubber seals, while the 1976 to 1985 engines used thicker 3/8-inch seals.

Bowtie splayed valve heads (PN 10185040) use valve cover gasket PN 10185043.

Oil Pan Gaskets

Determine which side of the engine is set up for the oil dipstick location. You’ll want an oil pan that matches the block’s dipstick position. Oil pan gaskets are made to match whichever side the dipstick fits, and the block, pan, and the oil pan gaskets all must match. Some replacement and Bowtie blocks were made with provisions to put the dipstick on either side.

Gen I engines from 1955 through 1985 with two-piece rear main seals used four separate gaskets to seal the oil pan to the bottom of the block. Check the seal thickness used to seal the front of the oil pan to the bottom sealing surface of the timing chain cover. Two different thicknesses have been used over the years, and you may also have an oil pan that came from a different year engine than the block you are using. It’s no problem; most gasket sets come with both gasket sizes.

Here’s how to tell which front pan gasket to use: On engines from 1955 to 1974, a 1/4-inch-thick gasket was used, and from 1975 to 1985, a 3/8-inch-thick gasket was used. Take the oil pan you are going to use and place a straightedge across the pan rails and over the front gasket half-moon opening. Now measure the distance from the seal surface to the bottom of the straightedge. If the distance is 21/4 inches, use the 1/4-inch-thick seal. If the distance is 23/8 inches, use the 3/8-inch-thick seal.

Oil pans and oil pan gaskets for 1986-on one-piece rear main seal engines are different from those found on pre-1986 two-piece rear seal blocks. The one-piece seal blocks use a one-piece neoprene gasket (PN 10108676) to fit the redesigned oil pan found on Gen I one-piece seal engines. Use metal oil pan rail reinforcements (PN 12553058 LH and 12553059 RH) with one-piece-style oil pans. Gen II L99, LT1, and LT4 pans can use oil pan gasket PN 10108676.

Gasket Sealants

Since the head bolts go through the water jackets on production blocks, it is necessary to use thread sealant on these bolts to prevent water from seeping up the bolt columns. Sealants are used elsewhere in the motor, but use these sealants sparingly.

Excessive sealants are pushed out as bolts are torqued down and pieces can begin to circulate in the motor. They can wind up clogging the oil pickup screen and cutting off the oil supply. Blobs of sealant can move into small passages and prevent oil circulation in other parts of the motor. Gasket cements hold a gasket where you need it, and there is less chance of any excess gasket cement squeezing out and moving through the motor.

Gen I and Gen II engines with a one-piece rear main seal and matching crank use a single, one-piece oil pan gasket. These are also now available for earlier blocks as well.

To help seal the first-generation small-block oil pans, Chevrolet Performance offers these oil pan rails that help spread the torque of the bolts over the mounting area.

Recommended Bolt Torque

If the engine is going into a vehicle that has an oxygen sensor in the exhaust system, use sealants that are oxygen sensor safe. Some of the sealants on the market produce gases while curing that can damage the oxygen sensor.

Fasteners

Each bolt and stud manufacturer, whether it is from Chevrolet or an aftermarket company specializing in fasteners, has a recommended torque value or stretch value for each type of fastener. Follow the manufacturer’s recommendation for the proper amount of torque or stretch required for the bolt or stud. Also, each fastener type, depending on its application, requires some type of lubricant on the threads in order to achieve the proper torque or stretch amounts. This lubricant could be sealants, oils, anti-seize, or some form of moly-based lubricant. Follow the recommendations.

Each fastener that is torqued must be drawn up to its recommended torque value in stages and in the proper bolt-torquing sequence. This is especially important when tightening main cap fasteners, head fasteners, and rod bolts. Follow the recommendations, take your time, and double-check your work.

Of equal importance is that every fastener must be clean. Clean the threads and holes in the block and remove any rust, corrosion, and old sealants. If a threaded hole is damaged, it needs to be repaired; the threads on a fastener must be spotless as well. Make sure that the fastener threads are not damaged or stripped.

Like many gaskets, if you cannot find a specific fastener from Chevrolet any more, chances are that one of the aftermarket fastener companies such as ARP or Milodon will have what you need.

Main Cap Bolts and Studs

Small-journal Gen I blocks used a different length main cap bolt than later medium- and large-journal Gen I blocks, which were about 1/4 inch longer. Use the correct bolts or aftermarket studs. Also, the main cap bolt spacing is different between the small, medium, and large journal blocks, and so the main caps are not interchangeable between the small, medium, and large journal (400) blocks.

The production main cap bolts used by Chevrolet work just fine in all street applications and you don’t need to use a stud kit in a stock or street performance engine. Stud kits offer the advantage of reducing the amount of wear and tear on block threads, if you are frequently tearing the motor down. Some race situations can benefit by using a stud kit, especially if you are using a two-bolt block. A main cap stud kit adds strength to the bottom end of the two-bolt block. In large nitrous, supercharger, or turbocharger, high-RPM and high-power applications, a four-bolt block with a stud kit can help. Nodular-iron caps are stronger than the production gray iron caps, and steel caps are stronger still. Also, a splayed main cap offers more strength than a straight main cap.

A four-bolt production block uses 10 inner main cap bolts (PN 3932480) and 6 shorter outer bolts (PN 3877669). Chevy Performance offers a Main Bearing Bolt Kit for its Sportsman Blocks as PN 12480108. These bolts are Grade-8 with 12-point heads and an oxide coating.

If you have a small main journal (2.30 inches) two-bolt block, you can use windage tray mounting studs in five of the main cap bolt positions. This stud (PN 3872718) is 51/4 inches long. A similar windage tray stud for use with 2.45 main journal blocks is PN 14087508. These studs are 5⅝ inches long and can be used with two-bolt blocks or as the inner studs on a four-bolt block.

Four-bolt blocks with straight main caps not using a windage tray can use the 7/16-inch main cap stud kit (PN 10185033). PN 14011001 stud is used in the inner position and PN 14011002 in the outer stud position. These outer studs should not be used on splayed main bearing caps. PN 10046007 is a mounting bolt for the oil pump, which has a stud portion that holds the rear edge of a windage tray. Use a hardened steel flat 7/16-inch stud washer (PN 14087508) with 12-point 7/16-inch x 20 nut (PN 3942410) or 6-point 7/16-inch x 20 nut (PN 3942410).

Two main cap stud kits are offered for four-bolt blocks. PN 14011039 has all of the studs required for one block with straight main caps but does not include the washers and nuts.

Main stud kit PN 10185033 includes the washers and nuts and has 10 (7/16-inch) inner studs, 14 (7/16-inch) outboard studs, and 4 (3/8-inch) outboard studs, all of which are made from 4340 steel.

Cylinder Head Bolts and Stud Kits

Cylinder head/block deck dowel pins are used to help position the head on the block. These dowel pins are 5/16 x 9/16-inch (PN 585927). Offset dowel pins (available from aftermarket suppliers) are sometimes used by experienced engine builders and machinists to relocate the combustion chambers on the head in relation to the cylinder barrels.

Gen I production small-blocks use three different length head bolts to secure the cylinder heads to the blocks. Long head bolts (PN 10168525) are 7/16-14 x 3.75 inches. You need 14 of these. The medium-length bolts (PN 10168526) are 7/16-14 x 3.00 inches. Four are required per motor. The bottom row of short head bolts use PN 10168527 and are 7/16-14 x 1.75 inches. Sixteen are used. A kit with all of the bolts is available as PN 12495499.

Aluminum D-port Corvette heads PN 10185086 and 10185087 (casting number 10088113) require different head bolts with flat washers under the bolt head to protect the aluminum surface of the heads. Use long bolt PN 10168525 (7/16-14 x 3¹³⁄₁₆ inches), medium-length bolt PN 10168526 (7/16-14 x 3¹⁄₁₆ inches), and short bolt PN 10168527 (7/17-14 x 1³⁄₄ inches). These bolts come with the correct flat washer.

A cylinder head stud kit is offered under PN 14014408 and can be used on conventional production cast-iron and aluminum raised runner Bowtie heads. This kit does not include flat washers or nuts. Short head studs are available individually as PN 14011035 (7/16-14 x 2.69 inches). Long-length head studs are PN 14011036 (7/16-14 x 4.73 inches). The medium-length studs are PN 14011037 (7/16-14 x 3.99 inches).

These head studs can be used with 1038 steel stud nut PN 3942410, which has six points and is 7/16-20, or the 12-point 4037 steel stud nut PN 14044866 (7/16-20). Both of these stud nuts are magnafluxed at the factory. Hardened steel flat washers are under PN 1005115, which has a 0.45-inch ID and 0.750-inch OD and should be used on Phase 6 Bowtie aluminum heads for clearance, or on other heads, you can use flat washer PN 14011040, which is 0.45-inch ID and 0.778-inch OD.

GM head stud kits are not made for the Bowtie 18-degree, 15-degree, splayed valve, or SB2 race heads. These must be obtained from aftermarket suppliers.

Something to consider when using head stud kits is that you may not be able to remove the cylinder heads from the engine once the engine is in your vehicle. Depending on the size of your engine compartment, firewall position, air conditioner, and heater box size and location, brake boosters, etc., you may not have enough room to slide the heads on or off the studs. You may have to remove the engine from the vehicle in order to get the heads off.

If you are using small-block heads on a race motor and these heads have been angle milled (which is quite common), remember to have the surfaces on the heads, where the head bolt holes are, spot faced to the correct angles to match the angle milling of the head deck surface. If you do not do this or if your machinist fails to do this after angle milling the cylinder heads, the heads of the bolts (or the nuts used with a head stud kit), do not bear down on the head surface squarely and correctly.

Gen I and II engines used three different lengths of head bolts.

If you need to refresh your 350 HO engine, Chevy Performance offers a complete gasket kit (PN 19201171) that includes head gaskets, oil pan, intake, fuel pump, timing chain cover, rear main seal, and valve cover gaskets. (Photo Courtesy Chevrolet Performance)